Fluorescence scanners generally scan samples via stimulation by a light beam at an excitation wavelength, in a one or two-dimensional manner. The resulting stimulated fluorescent emission, which typically occurs at a different wavelength or wavelength band, is then detected. One type of scanner requires movement of an excitation beam in one axis and movement of a mechanical stage in an orthogonal axis so that successive straight line scans sequentially cover a two-dimensional area of the sample. Alternatively, the stage may be in a fixed position and the laser beam may be scanned along two axes. Also, the sample may be translated on an X-Y stage and viewed with a microscope or similar fixed optical viewer.
The movement of a light beam to effect scanning in most fluorescence scanners is generally accomplished via galvanometer scanners and rotating polygonal mirrors. These devices are best suited for wide angle scanning, as is necessary for detecting fluorescence emission from planar DNA sequencing gels.
It is important in certain applications to cause stimulation of fluorescence emission from a constant angle at all points of the specimen being scanned. There are inherent difficulties in adapting the above scanning systems to such a situation because the scanning beams have some rotational motion and distortions of fluorescence imaging at various locations of the specimen may occur. Aberrations may be minimized through an f .THETA. lens which, in conjunction with one of the above scanning mechanisms, provides correction of scan angle and speed and allows for scanning of a flat specimen with an incident beam. Such lenses are quite expensive, however. The costs of some of these scanning mechanisms is also very high.
A wide variety of scan formats is necessary for many research and diagnostic applications. In particular, smaller experimental formats are emerging, such as the scanning of nucleic acid samples on small chips and electrophoresis within capillary tubes. Miniaturization of the effective scanning areas of existing fluorescent scanners requires intricate and expensive adaptation of optical assemblies and is, therefore, not feasible.
It is also desirable to increase scan speed without compromising resolution in order to scan many samples in a short period of time. Existing scanners are limited with respect to scan speed and resolution because of their numerous components and the high mass of their optical assemblies, and also because they are optimized to particular scan angles and sample sizes.
It is therefore an object of the present invention to provide a versatile fluorescent scanner of simple, lightweight, low-cost design for rapid scanning of a small format sample from a constant angle.